Superconductivity and local structural correlations in Ba_1-xK_xBiO₃

Potassium-doped barium bismuthate (Ba_1-xK_xBiO₃) exhibits a maximum superconducting transition temperature (T_c) of just above 30 K and was the first high-T_c oxide to be discovered. Although Ba_1-xK_xBiO₃ is generally thought to be a conventional s-wave superconductor, the pairing mechanism is still under debate, and both electron-phonon coupling and charge-disproportionation effects may play a role. Our recent diffuse x-ray scattering measurements of the local structure, complemented by Monte Carlo modeling, demonstrated that disproportionation is absent in the metallic/superconducting doping regime [1]. Instead, this work revealed nanoscale structural correlations that break inversion symmetry, with profound implications for the electronic physics, including the pairing mechanism. Here we report on our efforts to extend the diffuse scattering measurements to temperatures below T_c and to additional doping levels. We will also describe recent complementary inelastic x-ray scattering experiments aimed at elucidating the observed structural features.

[1] S. Griffitt, M. Spaić, J. Joe, Z. Anderson, D. Zhai, M. J. Krogstad, R. Osborn, D. Pelc, and M. Greven, Nat. Commun. 14, 845 (2023)